In conventional offshore oil and gas production systems, subsea equipment is operated using hydraulic fluid provided via lines commonly referred to as umbilicals. A standard subsea hydraulic fluid power delivery system relies on hydraulic fluid in umbilicals and subsea accumulators in which hydraulic energy is accumulated. Fluid is mobilized within the system in response to demands at the subsea equipment. The mobilization of fluid in the umbilical refers to the flowrate at which fluid can be delivered through the umbilical over a distance in response to a demand. This is dependent on the umbilical geometry, including, but not limited to, length, inner diameter, the speed of sound in fluid and the pressure difference between the surface and the subsea equipment location. As a result, an undesirable delay or lag in response time often occurs when the umbilical is quite long. Compression of nitrogen is used to store hydraulic energy in the form of fluid under pressure so that the fluid in the accumulator can meet system demands until fluid in the umbilical can be mobilized. However, the efficiency of nitrogen for compression deteriorates rapidly with increasing absolute pressures in deep water. In certain cases, stored hydraulic energy at a subsea location adversely can delay lowering of the subsea hydraulic pressure.
There exists a need for a subsea hydraulic fluid pressure regulation system which can meet or respond to hydraulic fluid demands by increasing or decreasing hydraulic fluid pressure in a subsea location more quickly.